html, body {
  height: 100%;
  background-color: #000;
  // box-shadow: 0 -1000px #fff, 0 1000px #fff, 1000px 0 #fff, -1000px 0 #fff;
}
#app {
  overflow: hidden;
  height: 100%;
}
.mask {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0,0,0,.7);
  text-align: center;
  font-size: 18px;
  color: #fff;
}
.center {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  margin: auto;
}
.center .close_btn {
  position: absolute;
  top: -40px;
  right: -40px;
  width: 40px;
  height: 40px;
  background: transparent url('../assets/close_btn.png') center no-repeat;
  background-size: 60%;
  border-radius: 50%;
}
.boxShadow {
  width: 68%;
  height: 50%;
  background-color: red;
  border-radius: 2%;
  box-shadow: 3px 3px #ff0,
              3px -3px #ff0,
              -3px 3px #ff0,
              -3px -3px #ff0;
}